Conventionally, a sheet folding device including a sheet transportation means for drawing out sheets of paper stacked on a sheet loading unit one at a time so as to transport them, a sheet stopper for preventing the sheets transported by the sheet transportation means from traveling, and a sheet folding means for pinching and folding a bent portion of the sheet that has been prevented from traveling by the sheet stopper and partially bent as a result, is well known (Patent Document 1).